1. Field of the Invention
The present invention relates to a process for preparing a reactive tinting compound and the use of such a compound to manufacture the tinted soft contact lenses. More particularly, the invention relates to a tinted hydrophilic soft contact lens containing covalently bonded dye that does not leach out and fade after multiple autoclave sterilization.
2. The Prior Arts
Many different processes have been disclosed to produce tinted or color ophthalmic lenses, such as contact lenses, for various functional purposes. For example, the tinted lens not only can serve the purpose of changing the apparent color or the iris of the wearer but also offer the lenses to be easily located in the clear solution within the lens storage, disinfecting, or cleaning container.
Usually, the tinting dye can be imparted to the lens either before or after the lens forming materials are polymerized. A conventional method to impart color to the contact lens is to dissolve or disperse the inorganic pigment or the long chain organic dye in the monomer precursor or in the polymer matrix before the lens is formed. The inorganic pigment or the long chain organic dye is entrapped in the lens to give the desirable color. However, this method is inadequate for coloring the hydrophilic soft contact lens because the great water content in the lens usually induces a migration or leaching of the colorant. This undesirable migration or leaching can be accelerated during the high-pressure heat sterilization treatment as commonly applied with the hydrophilic soft lens.
The use of a water insoluble dye in the soft lens to alleviate the aforementioned shortage is proposed in U.S. Pat. No. 4,252,421. The tinted lens is prepared by heat curing hydrophilic lens forming monomers with the presence of the water insoluble phthalocyanine dye such as the copper phthalocyanine. The phthalocyanine dye is entrapped in the finished lens and believed to be stable at a maximal hydration content of 35.7%. Unfortunately, this water insoluble phthalocyanine dye still can leach out of the lens with the use of the hydroxyethyl methacrylate (HEMA) as the hydrophilic comonomer and with a water content of 40%. Moreover, the leaching problem may worsen with greater water content.
The use of copper phthalocyanine pigment (Color Index Pigment Blue 15) to prepare a tinted contact lens is also disclosed in U.S. Pat. No. 6,149,842. The copper phthalocyanine pigment is firstly dispersed in an aqueous solution containing the polyvinyl alcohol (PVA) as a dispersing agent, and then mixed with the crosslinkable PVA precursor and subsequently photopolymerized in the mold to form the lens. No detail in performance of this dye in the as-formed lens is disclosed. As described previously, the leaching occurred at large water content is a potential problem.
A similar concept is disclosed in U.S. Pat. No. 5,516,467 in which a vat dye (for example, C. I. Vat Blue 6) is converted to a leuco compound and dissolved in the hydrophilic N,N-dimethyl acrylamide monomer to prepare a tinted monomer solution. Then this solution is polymerized with other constituents under heat to form the lens and subsequently boiled to convert the solubilized leuco compound into an insoluble vat dye. Although the vat dye is not covalently bonded with the lens forming materials, it is reported to have a great stability and does not fade after 200 hours in the boiling water. However, the fixed vat dye may again be converted to the soluble leuco compound under a suitable alkaline condition and be unevenly reacted under an acid environment.
The other method for imparting color to a contact lens is to coat the finished lens by printing or transfer printing method. Basically, this method usually applies coloring ink containing solvent-based colorant to the lens with a silicone rubber pad. The transferring method is questionable because it could not give an unblemished, solid covering of colorant on the dry lens surface. Many attempts have been suggested to solve this problem. Some propose to use multiple transfer printing steps to coat mottled color dots onto the lens surface. Some apply pigment/monomer suspension to the mold that is stamped or printed with specific geometries and spacing, and then form the tined lens with the conventional spin casting technique as disclosed in U.S. Pat. No. 4,640,805. Despite the ease of the blemish defect, all these modified methods suffer the potential risk of colorant migration during autoclave sterilization because of using the non-covalently bonded dyes. As a result, the reactive tinting dye that can be copolymerized with lens materials is preferred to prevent leaching of the dye from the lenses during various service environments.
A reactive dye used for preparing the transfer printing ink to remedy the previous migration shortage is disclosed in U.S. Pat. No. 5,352,245. The patent proposes using a reactive dye, e.g., Ramazol Black B, together with the polyvinylpyrolidone binder and a non-ionic surfactant to prepare the ink and then transfer printing it onto the hydrophilic contact lens to form the tinted lens with the desired pattern. The reactive dye is supposed to be covalently bonded with the lens materials after subsequent immersion in the basic solution. Yet no performance detail of the tined lens is disclosed. In addition, the method is tedious and has the shortage similar to that present in the soaking-to-fix techniques.
Many patents including U.S. Pat. Nos. 4,559,059, 4,468,229, 4,157,892, 4,891,046, 4,553,975, 4,929,250, 5,292,350, and 5,480,927 propose the lens tinting method by soaking the formed lens together with the reactive dye in the alkaline solution to chemically bond the dyes with the lens materials. The reactive tinting dye can either be premixed with the monomer mixtures before the polymerization step or be added to the basic solution after the lens is polymerized. Regardless of different reactive dyes and procedures proposed in these patents, they are usually time-consuming and require multiple steps, such as neutralization, extraction, and rinsing steps to tint the lens. Additionally, the processing variables should be carefully controlled to prevent uneven dispersion and colorization.
A more promising method to add the desirable color to the lens is to covalently bond the monomer or prepolymer with the reactive dye first and then introduce this functionalized precursor to the mold and cure. This technique will greatly alleviate the processing problems described in soaking-to-fix methods. A few of patents, for example, U.S. Pat. Nos. 4,252,421, 5,944,853, 5,938,795, 5,871,675, 6,149,692, 4,795,794, and 6,162,844, use the aforementioned technique to chemically fix the dye with the lens forming materials before the polymerization step. The differences among these patents are mainly on types of reactive dye and precursor reacted. Although advantages are obtained in these patents, some patents still have problems such as the low yield and tedious purification step. For example, a vinyl-sulfone type reactive dye (C. I. Reactive Black 5) that reacted with the hydroxyethyl methacrylate to prepare the dye-monomer compound with no activating step used is disclosed in U.S. Pat. No. 5,944,853 but a very low yield is obtained. This dye-monomer compound is not used to prepare the soft contact lens as described in U.S. Pat. No. 5,938,795 from the same inventors of U.S. Pat. No. 5,944,853.
U.S. Pat. No. 6,149,692 issued to Lally et al. discloses a method of contacting a functionalized dye with a high molecular weight crosslinkable polymer precursor, dispensing the solution into a mold and applying radiation, thereby forming a molded article having dye covalently boned to the polymer backbone. The dye essentially copolymerizes with the polymeric precursor. The polymer precursor (such as PVA) used in Lally et al. has an average molecular weight of at least about 2000. The PVA oligomer used by Lally et al. does not have reactive vinyl groups in the beginning. Therefore, a so-called polymer precursor functionalizer is prepared first and then the functionalizer is reacted with the PVA oligomer to introduce the crosslinkable vinyl group to the PVA molecules. The crosslinkable polymer precursor is then purified and subsequently reacted with the activated dye. There are multiple procedures involved in preparing the crosslinkable PVA-DYE compounds.
In summary, the previous patents disclosed for the production of tinted contact lenses usually suffer one or more undesired nature such as long processing time, low degree of conversion, leaching of weakly bonded dye, fading, inconsistent shade of the tinted lens, and tedious reacting or purification process. Henceforth, there exists a need for preparing the tinted contact lens with a great color fastness but without aforementioned shortages.